An antenna array with a plurality of antennae is widely used in a communication apparatus, such as a transceiver, a transmitter or a receiver, and the phase of the antenna array can be controlled to have a specific main direction for radiating signals (i.e. the radiation field pattern can be controlled). The conventional controlling manner for the antenna array can be implemented by a plurality of phase shifters or a plurality of PLLs, wherein each neighbor two of the PLLs are coupled to each other.
Referring to FIG. 1A, FIG. 1A is a schematic diagram of a conventional phase controller used in a communication apparatus. In FIG. 1A, the communication apparatus 1 comprises a plurality of phase shifter PS_1 through PS_n and a plurality of antennae ANT_1 through ANT_n, wherein n is an integer larger than 1. The phase shifters PS_1 through PS_n form a conventional phase controller, and the antennae ANT_1 through ANT_n form an antenna array, wherein each neighbor two of the antennae ANT_1 through ANT_n have a separated distance d.
Each of the phase shifters PS_1 through PS_n receives a first transmitted signal and shifts a phase of the transmitted signal, so as to generate a plurality of transmitted signals with different phases ϕ0 through ϕn to the corresponding one of the antennae ANT_1 through ANT_n. The phases ϕ0 through ϕn can determine the angle θ (in respective to a vertical axis y), or a main radiating direction MD of the antennae array, and the distance d between wave fronts of each neighbor two of the antennae ANT_1 through ANT_n is related to the angle θ of the antennae array. Therefore, by controlling the phases ϕ0 through ϕn, the radiation field pattern of the antenna array can be determined.
Next, referring to FIG. 1B, FIG. 1B is a schematic diagram of another one conventional phase controller used in a communication apparatus. The difference between the communication apparatuses 1′ and 1 is that the configuration of the phase shifters PD_1 through PD_n of the communication apparatus 1′ is not the same as that of the phase shifters PS_1 through PS_n of the communication apparatus 1. Specifically, the communication apparatus 1′ adopts the step phase shift configuration of the phase shifters PD_1 through PD_n, each of the phase shifters PD_2 through PD_n receives the transmitted signal being shifted with the phase Δϕ by the previous one phase shifters PD_1 through PD (n−1), and the phase shifter receives the transmitted signal. By controlling the phase Δϕ, the radiation field pattern of the antenna array can be determined.
The shifted phases of the phase shifters in different frequencies are not identical to each other, and the phase shifters have problems of phase imbalance and gain dis-match. Thus, the transmitted signals which are expected to have fixed differential phases may have phase errors and amplitude errors, and it causes the desired radiation filed pattern of the antenna array is not correct.
As mentioned above, another one conventional controlling manner for the antenna array adopts a plurality of PLLs, wherein each neighbor two of PLLs are coupled, and the control signals can be input into the voltage controlled oscillators (VCOs) of the PLLs to control the phase of the antenna array. However, this conventional controlling manner for the antenna array does not comprise a reference signal source with the high precision and the low phase noise, and it uses the coupled VCOs for injection and locking, thus resulting that the high phase noise may exists in the output signals of the VCOs, and the output frequency is not accurate.